Self-temperature-limiting carbon-coated foil and preparation method thereof

Abstract

The invention belongs to the technical field of lithium ion batteries, and discloses a self-temperature-limiting carbon-coated foil and a preparation method thereof. Wherein the carbon-coated foil comprises an aluminum / copper foil base material and a carbon-coated layer with a self-temperature-limiting function. The carbon-coated layer is coated and cured by carbon slurry, and the carbon slurry is prepared by dispersing 5-15 parts of a conductive agent, 10-30 parts of a binder, 1-10 parts of a positive temperature coefficient material and 45-84 parts of a solvent. According to the prepared self-temperature-limiting carbon-coated foil, when thermal runaway happens to a battery, the temperature rises sharply, and when the Curie temperature of an added positive temperature coefficient material is reached, the resistance of the self-temperature-limiting carbon-coated layer in the self-temperature-limiting carbon-coated foil rises sharply in an exponential level mode, electrons are isolated between the positive and negative electrode material layers and a current collector, the electrons cannot be transmitted, and the interior of the battery is in an open circuit state; the temperature is prevented from further rising, the overheating risk of the battery is reduced, the safety of the lithium ion battery is greatly improved, and the lithium ion battery has extremely high practical value in the fields of new energy automobiles and energy storage.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, specifically to a self-limiting temperature coated carbon foil and its preparation method. Background Technology

[0002] With the large-scale application of lithium-ion batteries in new energy vehicles and energy storage systems, their thermal safety has become a key bottleneck restricting the industry's development. Carbon-coated aluminum / copper foil, as an important means of improving battery electrochemical performance, has been widely used to improve the interfacial contact between current collectors and electrode materials, reduce internal resistance, and inhibit electrolyte corrosion. In recent years, to further improve battery safety, some studies have begun to explore introducing positive temperature coefficient (PTC) materials into the carbon coating layer to achieve a resistance jump when the temperature rises, thereby cutting off the current in the early stages of thermal runaway.

[0003] However, existing self-regulating carbon-coated aluminum foil technologies still have several significant drawbacks: First, the PTC material systems used are relatively limited, mostly confined to polymer-based PTC materials (such as EVA and polyurethane). These materials have insufficient resistivity change rate at high temperatures, poor repeatability, and a narrow Curie temperature range, making it difficult to adapt to the thermal safety requirements of different battery systems. Second, the conductivity balance of traditional PTC carbon coatings at room temperature and high temperature has not been well resolved, often sacrificing conductivity under normal operating conditions for safety characteristics. Third, the PTC material in existing processes has poor dispersion uniformity and is prone to agglomeration, leading to inconsistent local resistance changes and affecting overall circuit breaking reliability. In addition, most solutions fail to balance the mechanical strength, adhesion, and electrochemical stability of the carbon coating, making it prone to coating peeling or failure during actual battery cycling.

[0004] Therefore, developing a highly reliable self-regulating carbon-coated current collector with a wide temperature range, high resistivity change rate, good conductivity-insulation switching characteristics, and compatibility with existing battery processes remains a technical challenge that urgently needs to be solved in this field. Summary of the Invention

[0005] In view of this, the present invention provides a self-regulating temperature-coated carbon foil and its preparation method to solve the problems mentioned in the background art.

[0006] To achieve the above objectives, the present invention provides the following technical solution: In a first aspect, the present invention provides a self-regulating carbon-coated foil, comprising an aluminum / copper foil substrate and a carbon coating layer having a self-regulating function. The carbon coating layer is formed by coating a carbon slurry onto the surface of the aluminum / copper foil substrate and curing it. The carbon slurry is prepared by dispersing 5-15 parts of a conductive agent, 10-30 parts of a binder, 1-10 parts of a positive temperature coefficient material, and 45-84 parts of a solvent. The positive temperature coefficient material is selected from at least one of ethylene-vinyl acetate copolymer, polyurethane resin, ethylene-acrylate copolymer, and rare earth-doped nano-barium titanate.

[0007] Furthermore, the conductive agent is at least one of carbon black, carbon nanotubes, graphite, and graphene.

[0008] Furthermore, the adhesive is at least one of acrylic resin, polyimide resin, epoxy resin, and polyvinylidene fluoride.

[0009] Furthermore, the solvent is at least one selected from water, N-methylpyrrolidone, methanol, ethanol, propanol, isopropanol, and n-butanol.

[0010] Furthermore, the Curie temperature of the positive temperature coefficient material is 60-80℃.

[0011] Furthermore, its curing temperature is 90-110℃; preferably, the curing temperature is 80-100℃.

[0012] Furthermore, the thickness of the carbon coating layer is 0.5-1 μm, and the thickness of the foil is 4-13 μm.

[0013] Furthermore, its foil material is aluminum foil or copper foil.

[0014] Secondly, the present invention discloses a method for preparing the self-regulating temperature-controlled carbon foil as described above, including a method for preparing the carbon coating slurry, as follows: Under normal temperature and pressure, the adhesive is uniformly dispersed in the solvent to obtain the first mixture; The conductive agent and the positive temperature coefficient material are added to the first mixture. After thorough dispersion, demagnetization, and sieving, the carbon coating slurry is obtained.

[0015] Compared with the prior art, the beneficial effects of the present invention are: (1) The carbon-coated foil with self-limiting temperature function provided by the present invention has a high-temperature self-protection function: when the battery temperature exceeds the Curie temperature (60–90℃) of the PTC material, the resistance of the carbon coating layer rises sharply, realizing the automatic cut-off of the electronic channel and effectively preventing the further development of thermal runaway. (2) Maintain normal performance: Within the normal temperature range, the carbon coating layer still has excellent conductivity and interfacial contact performance, and does not affect the rate performance and cycle life of the battery. (3) Enhanced interface stability: The carbon coating layer, as a buffer layer, continues to play its traditional advantages such as reducing internal resistance, enhancing adhesion, and resisting corrosion; (4) Strong material compatibility: It can use a variety of PTC materials (such as EVA, polyurethane, rare earth doped barium titanate, etc.) to adapt to the safety temperature threshold of different battery systems. Attached Figure Description Figure 1 The data show the battery internal resistance of the carbon-coated foil obtained in each embodiment and comparative example at different temperatures. Detailed Implementation

[0016] To facilitate understanding of the present invention, a more comprehensive description will be given below with reference to specific embodiments. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of the disclosure of the present invention.

[0017] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

[0018] The specific information of the raw materials used in the following examples and comparative examples is as follows: The acrylic resin is manufactured by Sichuan Yanyi New Materials Co., Ltd., and its brand name is BAP-S. The manufacturer of the polyimide resin is Kaifeng Quark New Materials Co., Ltd., and the grade is SI-3011. The manufacturer of polyvinylidene fluoride is Zhejiang Funolin Chemical New Materials Co., Ltd., and the grade is FL2032. The manufacturer of the carbon black is Jiangxi Black Cat Carbon Black Co., Ltd., and the grade is MS4010. The manufacturer of the carbon nanotubes is Qingdao Chaorui Nanomaterials Technology Co., Ltd., and the grade is CR7272. The graphene is manufactured by Qingdao Yanhai Carbon Materials Co., Ltd., and its brand name is HGP-3A. PTC material: The manufacturer of the ethylene-vinyl acetate copolymer is Lianhong New Material Technology Co., Ltd., and the grade is UL01833; The manufacturer of the polyurethane resin is Shanghai Bolino New Material Technology Co., Ltd., and the brand name is PU-9519S. The manufacturer of rare earth-doped nano barium titanate is Zhejiang Manli Nanotechnology Co., Ltd., and the grade is ML-N50. The manufacturer of the high-density polyethylene is Sinopec, and the grade is DMDA-8008. The manufacturer of low-density polyethylene is Sinopec, and the grade is DFDA-7042. All materials are commercially available, commonly used products.

[0019] It is understood that the above-mentioned raw materials and reagents are merely examples of some specific embodiments of the present invention, making the technical solution of the present invention clearer, and do not mean that the present invention can only use the above-mentioned reagents. The specific scope shall be determined by the claims. In addition, unless otherwise specified, "parts" in the examples and comparative examples refer to parts by weight.

[0020] Any range described in this invention includes the endpoint, any value between the endpoints, and any subrange consisting of the endpoint or any value between the endpoints.

[0021] Example 1 30 parts of acrylic resin were added to 45 parts of solvent (water and isopropanol in a 1:1 weight ratio) and mixed thoroughly to form a first mixture. 15 parts of a mixed conductive agent of carbon black and graphite (carbon black to graphite weight ratio 4:1) were added to the first mixture, followed by the addition of 10 parts of ethylene-vinyl acetate polymer. The mixture was then dispersed via high-speed dispersion and wet milling to prepare a carbon slurry. This carbon slurry was coated onto both sides of a 12 μm thick aluminum foil and cured at 90°C to obtain a 1 μm thick, self-limiting carbon-coated aluminum foil with a Curie temperature of 60°C.

[0022] Example 2 Ten parts of polyimide resin were added to 84 parts of solvent (water and n-butanol in a 1:1 weight ratio) and mixed thoroughly to form a first mixture. Five parts of a mixed conductive agent of carbon black and carbon nanotubes (carbon black to carbon nanotubes in a 3:1 weight ratio) were added to the first mixture, followed by the addition of one part of polyurethane resin. The mixture was then dispersed via high-speed dispersion and wet milling to prepare a carbon slurry. This carbon slurry was coated onto both sides of a 13 μm aluminum foil and dried and cured at 100°C to obtain a carbon-coated aluminum foil with a self-limiting temperature function, 0.8 μm thick on both sides, and a Curie temperature of 70°C.

[0023] Example 3 20 parts of polyvinylidene fluoride (PVDF) were added to 67 parts of N-methylpyrrolidone and stirred until homogeneous to form a first mixture. 8 parts of a mixed conductive agent of carbon black and graphene (mass ratio of carbon black to graphene 7:1) were added to the first mixture. 5 parts of rare-earth-doped nano-barium titanate were then added, and the mixture was dispersed by high-speed dispersion and wet milling to prepare a carbon slurry. This carbon slurry was coated onto both sides of a 5 μm thick copper foil and dried and cured at 120 °C to obtain a 1 μm thick carbon-coated copper foil with self-limiting temperature on both sides. The Curie temperature of this carbon-coated / copper foil was 80 °C.

[0024] Comparative Example 1 Compared with Example 1, the only difference is that the ethylene-vinyl acetate polymer is replaced by an equal amount of solvent (water and isopropanol in a weight ratio of 1:1).

[0025] Comparative Example 2 Compared with Example 1, the only difference is that the ethylene-vinyl acetate polymer is replaced in equal amounts with high-density polyethylene (e.g., Tc>120°C).

[0026] Comparative Example 3 Compared with Example 1, the only difference is that the ethylene-vinyl acetate polymer is replaced in equal amounts with low-density polyethylene (e.g., Tc < 50°C) PTC material.

[0027] Comparative Example 4 The only difference from Example 1 is that the amount of ethylene-vinyl acetate polymer added is 0.5 parts.

[0028] Comparative Example 5 The only difference from Example 1 is that the amount of ethylene-vinyl acetate polymer added is 15 parts.

[0029] Performance testing The battery internal resistance of the carbon-coated foil obtained in each embodiment and comparative example was tested at different temperatures, and the results are shown in [the table below]. Figure 1 .like Figure 1 As shown, in Comparative Example 1, without the addition of PTC material, the battery's internal resistance changes very little at various temperatures. Comparative Example 2 shows that after replacing the PTC material with a material with a higher Curie temperature, the battery's internal resistance only undergoes a sudden change after 120°C. At this point, the internal side reactions of the battery intensify, potentially leading to significant irreversible capacity loss. Comparative Example 3 shows that after replacing the material with one having a Curie temperature <50°C, the battery's internal resistance undergoes a sudden change after 40°C. This temperature is frequently reached in summer, affecting the normal use of the battery. Comparative Example 4 shows that after changing the amount of PTC material added to 0.5 parts, although the battery's internal resistance still undergoes a sudden change at 60°C, the change is small and insufficient to support the condition of internal circuit disconnection. Comparative Example 5 shows that after changing the amount of PTC material added to 15 parts, due to the high proportion of PTC coating in the total content, the battery's internal resistance increases from 1.8 mΩ to 5.6 mΩ, failing to meet the requirements for normal battery use.

[0030] Although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

[0031] Therefore, the above description is only a preferred embodiment of this application and is not intended to limit the scope of this application; that is, all equivalent modifications made in accordance with the scope of the claims of this application shall be within the protection scope of the claims of this application.

Claims

1. A self-regulating temperature-limiting carbon foil, characterized in that, Its carbon coating layer is prepared from the following components in parts by weight: 5-15 parts of conductive agent 10-30 parts of adhesive 1-10 parts of positive temperature coefficient material Solvent 45-84 parts; The positive temperature coefficient material is at least one of ethylene-vinyl acetate copolymer, polyurethane resin, ethylene-acrylate copolymer, and rare earth-doped nano barium titanate.

2. The self-regulating temperature-regulating carbon foil according to claim 1, characterized in that, The conductive agent is at least one of carbon black, carbon nanotubes, graphite, and graphene.

3. The self-regulating temperature-regulating carbon foil according to claim 1, characterized in that, The adhesive is at least one of acrylic resin, polyimide resin, epoxy resin, and polyvinylidene fluoride.

4. The self-regulating temperature-controlled carbon foil according to claim 1, characterized in that, The solvent is at least one of water, N-methylpyrrolidone, methanol, ethanol, propanol, isopropanol, and n-butanol.

5. The self-regulating temperature-regulating carbon foil according to claim 1, characterized in that, The Curie temperature of the positive temperature coefficient material is 60-80℃.

6. The self-regulating temperature-regulating carbon foil according to claim 1, characterized in that, Its curing temperature is 90-110℃.

7. The self-regulating temperature-regulating carbon foil according to claim 1, characterized in that, The thickness of the carbon coating layer is 0.5-1 μm, and the thickness of the foil is 4-13 μm.

8. The self-regulating temperature-controlled carbon foil according to claim 1, characterized in that, Its foil material is aluminum foil or copper foil.

9. The method for preparing self-regulating temperature-controlled carbon foil according to any one of claims 1-8, characterized in that, The preparation method of the carbon coating slurry includes the following steps: Under normal temperature and pressure, the adhesive is uniformly dispersed in the solvent to obtain the first mixture; The conductive agent and the positive temperature coefficient material are added to the first mixture. After thorough dispersion, demagnetization, and sieving, the carbon coating slurry is obtained.

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